1. Field of the Invention
The invention relates to polyols for rigid polyurethane foams and more particularly relates to such aromatic polyester polyols which are made from the waste streams of dibasic acids, alkylene glycols and recycled or scrap polyethylene terephthalate.
2. Description of Other Relevant Compounds in the Field
It is known to prepare polyurethane foam by the reaction of polyisocyanate, a polyol and a blowing agent such as a halogenated hydrocarbon, water or both, in the presence of a catalyst. One particular area of polyurethane technology is based upon rigid polyurethane foams.
Rigid foams generally have good insulative properties and are thus desirable for use in building insulation. As with all building materials, it is desirable to provide rigid foams that are as fire resistant as possible. One approach to this goal is to modify the polyol.
Polyisocyanurate foams are a type which are considered to be fire resistant and show low smoke evolution on burning. However, polyisocyanurate foams tend to be brittle or friable. Various types of polyols have been devised to lower the foam friability, but what frequently happens is that the fire and smoke properties of the polyisocyanurate foam deteriorate. Thus, a fine balance exists between the amount and type of polyol one adds to a polyisocyanurate foam formulation in order to maintain maximum flame and smoke resistance while at the same time reach an improvement in foam friability. U.S. Pat. Nos. 4,039,487 and 4,092,276 describe attempts at this fine balance, although each has its disadvantages.
The recovery of polyalkylene terephthalate scrap or residues has long been practiced. U.S. Pat. No. 3,344,091 described a process for converting scrap polyester, such as polyethylene terephthalate (PET) into active prepolymer particles by mixing the scrap PET with the glycol originally used in preparing PET, with or without the additional presence of a lower dialkyl ester of the aromatic dicarboxylic acid whose dehydroxylated residues are present in the scrap PET. Chemical Abstracts (CA) vol. 84, paragraph 5638h, relates that British Pat. No. 1,458,486 teaches dialkyl terephthalates, such as dimethyl terephthalate (DMT), recovery by heating scrap PET with monohydric alcohols with a catalyst and a sequestering agent.
PET scrap may be recovered by depolymerization with glycols as seen in CA 78:160452n, abstract to East German Pat. No. 92,801. U.S. Pat. No. 4,166,896 teaches that a mixture of glycols and oligomers (such as lower molecular weight polyesters of terephthalic acid and a glycol) may be depolymerized (transesterified) by heating. Subsequently, ethylenically unsaturated dicarboxylic acids or their anhydrides are added and the mixture is heated again. An unsaturated polyester resin is produced. A suitable dicarboxylic acid is phthalic acid, the anhydride of which is also useful in this process.
Scrap polyalkylene terephthalate, such as polyethylene terephthalate is known to be incorporated into polyurethanes. For examples, U.S. Pat. No. 4,048,104 relates that polyisocyanate prepolymers for use in polyurethane products may be prepared by combining an organic polyisocyanate with polyols which are the hydroxyl-terminated digestion products of waste polyalkylene terephthalate polymers and organic polyols. A polyol ingredient which is the digestion product of polyalkylene terephthalate residues or scraps digested with organic polyols is also described in U.S. Pat. No. 4,223,068. Another case where terephthalic acid residues are employed is outlined in U.S. Pat. No. 4,246,365 where polyurethanes are made from polyesters containing at least two hydroxyl groups and terephthalic acid residues.
More relevant to the compounds of this invention is the solution proposed in U.S. Pat. No. 4,237,238. In this patent, a polyol mixture is prepared by the transesterification of a residue from the manufacture of dimethyl terephthalate with a glycol, which is then used to produce polyisocyanurate foams having a combination of a high degree of fire resistance with low smoke evolution, low foam friability and high compressive strength. The preparation of such a polyol mixture (from ethylene glycol and dimethyl terephthalate esterified oxidate residue) is described in U.S. Pat. No. 3,647,759. J. M. Hughes and John Clinton, in the Proceedings of the S.P.I. 25th Annual Urethane Division Technical Conference, Scottsdale, Ariz. (October 1979), describe other foams prepared from the polyols of U.S. Pat. No. 3,647,759.
U.S. Pat. No. 3,755,212 teaches air blown polyurethane foams prepared from ester-modified polyether polyols, a polyisocyanate and a polyurethane catalyst. The modifying agents for reaction with the polyols apparently are internal anhydrides of polycarboxylic acids, such as phthalic anhydride. Rigid polyurethane foams may be made from a fluid polyol made by hydrogenating a DMT process residue, then reacting the hydrogenation product with an alcoholic material, according to U.S. Pat. No. 3,892,796. Further, U.S. Pat. No. 4,186,257 reveals that high molecular weight polyurethanes from polyols linked with ester groups may be made by reacting diols with phthalic acid or DMT. Polybutylene terephthalate diols and polyhexamethylene terephthalate diols are also used.
Brominated ester-containing polyether polyols may be prepared by the sequential reaction of a polyether polyol with 4,5-dibromohexahydrophthalic anhydride and an alkylene oxide according to U.S. Pat. No. 4,069,207. Flame-retardant polyurethane foams are prepared using these modified polyols. Also relevant is East German Pat. No. 122,986 cited in CA 86:190834w which teaches that polyurethanes may be manufactured from polyester polyols made by condensation and transesterification of PET synthesis distillation residues with polyols, polyamino alcohols and fatty acid ester diols.
There is still a need for a rigid polyurethane foam that has a high flame resistance. Part of the problem with the polyols of U.S. Pat. No. 3,647,759 is that they are not very compatible with trichlorofluoromethane, the gas entrapped in closed-cell rigid foams, which accounts for the excellent insulating properties of these foams.